This patent application is not the direct outgrowth of federally sponsored research.
The invention is in the field of chemical reactor design, applied to the conversion of a solid (usually in the form of a slurry) to soluble products, which are subject to decomposition. The objective of the design is to obtain high conversion of the solids while maintaining low decomposition of the soluble product(s). Of particular interest in this application is the hydrolysis of cellulose and hemicellulose in the solid to form sugars. The solid may be a form of biomass, such as wood, or a product derived from biomass, such as paper. The cellulose and hemicellulose in biomass can be hydrolyzed using an acid or base catalyst to form sugars, which are soluble and subject to decomposition. In some cases it is desired to convert the hemicellulose while leaving the cellulose largely untouched, so that the cellulose can be subsequently converted to sugars using enzyme catalysts. This partial hydrolysis is often referred to as pretreatment or prehydrolysis.
Many reactor configurations have been considered in the published literature for the hydrolysis of biomass to sugars. The U.S. WWII effort to build a commercial reactor used a percolation reactor (Katzen, ISAF XIII, International Symposium on Alcohol Fuels Stockholm, Sweden, Jul. 3-7, 2000)1 in which an acid solution was applied to a bed of wood chips, and the sugar containing solution was withdrawn from the bottom of the reactor. Recently this type of reactor has been referred to as a xe2x80x98flow-throughxe2x80x99 reactor since the liquid flows through a bed of solids.
1 These refer to the citation numbers given in the Information Disclosure forms. 
Grethlein, U.S. Pat. No. 4,237,2262, discloses the use of a continuous co-current plug-flow reactor for the pre-hydrolysis of biomass.
Converse et al., U.S. Pat. No. 4,556,4303, discloses the use of a non-aqueous immiscible carrier fluid in a continuous plug flow reactor in order to convey the solids and, at the same time, increase the sugar concentration in the aqueous phase.
Wright et al., U.S. Pat. No. 4,615,7424 discloses the use of a series of fixed-bed flow-through reactors in which the liquid flow is switched so as to approximate counter-current flow.
Converse et al., U.S. Pat. No. 4,818,2955 discloses the use of a cyclone reactor in order to obtain counter-current flow between the solids and the liquid.
None of the above patents, and many others that teach methods of hydrolyzing cellulose and hemicellulose, make use of a cross-flow pattern. The patents referenced in this paragraph do speak of cross-current flow pattern. Torget et al., U.S. Pat. Nos. 5,424,4176; 5,503,9967; and 5,705,3698 discloses the use of a flow-through reactor for the prehydrolysis if lignocellulosic material. Specific to the current application the patent states. xe2x80x9cthe lignocellulose solids may be stationary, travel in a counter-current or cross-current fashion. . . . One can perform a solid-liquid separation in the flow-through system by using a screw-like device to cause the separation continuously during or at the end of prehydrolysis. Important to the process is the movement and removal of fluid during the prehydrolysis to separate soluble products as they are released from the solid lignocellulosic residue.xe2x80x9d (col. 6, lines 47-57, U.S. Pat. No. 5,503,996)7Furthermore it states: xe2x80x9csuch a reactor would have lignocellulosic material driven through the reactor while fluid is passed through the material, typically in a counter-current or cross-current manner. . . . Alternatively, the lignocellulosic substrate may be driven laterally while fluid is applied on top and allowed to percolate down to be removed at the bottom.xe2x80x9d (col. 6, line 66-col. 7, line 10, U.S. Pat. No. 5,503,996)7 The same statement can be found in the other two patents cited above, as well. O. Bobleter and H. Binder, German Patent No. DE 322507414, include, without comment on implimentation, the crossflow of water to solubilize and remove hemicellulose and portions of the lignin; it does not include the use of an acid catalyst nor the conversion of cellulose.
The current application uses these principles but differs from the patents cited above in the following aspects: 1) a unique geometry for effecting cross flow is described, 2) it is not limited to prehydrolysis, and 3) a computer simulation, employing cross-flow reactor
Recently the desirability of forcible expression of the liquid in a so-called xe2x80x98shrinking-bedxe2x80x99 reactor has been analyzed and demonstrated (Pettersson et al., 22nd Symp. on biotech, for fuels and chemicals, Gatlinburg, Tenn. May 7-11, 2000 Poster 3-489; Lee et al, Biores. Tech. 71, 29-39, 200010; Torget et al., Ind. Eng. Chem. Res., 39, 2817-2815, 200011).
Torget et al., U.S. Pat. No. 6,022,41912, discloses the use of a continous shrinking-bed flow-through reactor for the hydrolysis and fractionation of lignocellulosic biomass. The patent states that xe2x80x9cthe invention consists of a series co-current, counter-current or single pass, isolated stages . . . xe2x80x9d No mention is made of cross-current flow or withdrawal of the excess liquid in the radical direction.
The present invention is a reactor system for converting solids to soluble products which are subject to decomposition. An example is the conversion of biomass to such products, and includes the conversion of hemicellulosic, cellulosic and lignocellulosic substances to sugars. The term biomass, as used herein, means substances that are produced by photosynthesis, and includes hemicellulosic, cellulosic and lignocellulosic substances, both natural and processed, as well as natural or manufactured organic materials more broadly. Emphasis in the following discussion is placed on producing sugars for biomass, but the invention is broader, and is applicable to the conversion of any solid to liquid products which themselves are subject to decomposition.
The essence of the invention is that liquid, containing products from the reacting solids, is squeezed from the slurry by a compressive force and removed from the reacting zone by passage through an outer porous wall. This is done in order to minimize the residence time of the soluble products in the reactor, and thereby, minimize their decomposition. The liquid product stream may be thermally or chemically quenched as it is withdrawn to prevent further chemical reaction. The direction in which the exiting liquid moves is approximately perpendicular to the direction in which the slurry moves.
Liquid, possibly containing acid or base, may, or may not, be admitted into the reactor through the porous wall of the inner tube to aid in the washing of soluble product through the outer wall of the reactor. This liquid may assist in the temperature control of the reacting solids and may be mixed with steam. It may also contain chemicals such as a mineral acid to affect the reaction.